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Soluble fiber breaks down completely in water, and it helps control weight by producing a feeling of fullness. This type of fiber is found in fruits, such as strawberries, apples and oranges, which each contain approximately 3 grams of fiber per serving. Cucumber, celery and lentils are a few vegetables that contain soluble fiber, the latter containing 15 grams of fiber per cup. Oat bran, flaxseeds and nuts are also good sources of soluble fiber. Fruit and vegetable skins should be eaten when possible, as that is where most of the fiber is found.

Insoluble fiber mostly maintains its shape as it travels through the digestive system, which helps prevent constipation. Vegetables and whole grains are the best source of this type of fiber. Whole-wheat and whole-grain breads are high-fiber foods, and bran cereals containing 5 grams or more per serving are also an ideal fiber source. Seeds and nuts contain fiber, but they are high in calories as well. Dark, leafy vegetables, carrots and tomatoes are also good sources of insoluble fiber, with green vegetables typically containing higher amounts.